This invention relates to an ignition control device for an internal combustion engine, and particularly to an improved control device for obtaining a required ignition coil cut-off current even during a high rate acceleration of the engine.
An induction discharge type ignition device for use in an internal combustion engine is well known, in which high voltage energy is produced in the secondary side of an ignition coil by cutting off the electric current flowing through the primary winding of the coil so that a spark discharge is produced in an ignition plug connected to the secondary winding of the coil.
In general, the high voltage energy mentioned above depends upon the value of the current flowing through the primary winding of the ignition coil at a time when it is cut off. The current value will be referred to hereinafter as cut-off current.
In order to obtain enough energy to ignite the internal combustion engine, it is necessary to supply an electric current to the primary winding of the ignition coil until the cut-off current becomes adequate to ignite. The time from the start of current supply to the primary winding to the time at which the cut-off current reaches a value large enough to ignite, i.e., the current supply time, is determined by the battery voltage, the inductance on the primary side of the ignition coil and the resistance on the primary side of the coil, etc. Further, the ratio of the current supply time to the ignition period, referred to as a circuit closing ratio hereinafter, depends upon the number of revolutions of the engine. Therefore, the current supply time should be controlled such that a desired cut-off current value is obtained by taking these variables into consideration.
U.S. Pat. No. 4,041,912 and Japanese Kokai No. 17352/1983 disclose control devices capable of controlling the current supply time. Among others, the device disclosed in the latter controls the current supply time such that the ratio of the time period for which the current in the primary winding of the ignition coil is maintained at a predetermined value to the engine ignition period becomes constant.
However, since in such a conventional device, the calculation of the current supply timing is performed uniformly for every ignition period, a current supply time lone enough to ignite can not be obtained during a transient period such as a high acceleration of the engine or a large lead angle of the ignition timing in which the ignition period becomes shorter with the number of ignitions, resulting in a misfiring of the engine.